Maximum fuel economy is now the primary goal for designers of internal combustion engines in view of the current and ever increasing cost of gasoline.
The customary practice in designing and calibrating the fuel supply systems for internal combustion engines is to pre-schedule fuel flow according to some function of engine operating condition as measured on the engine during operation. On carburetor type engines the principal measured function is usually venturi pressure, and the fuel flow is primarily determined by this pressure (or depression) and secondarily the fuel flow may be determined by measuring various engine functions such as r.p.m., manifold vacuum, air flows, throttle position, etc., and controlling the fuel flow in accordance with some predetermined schedule.
Fuel control systems of the type described above depend on prior knowledge of how the engine will perform under all possible conditions of load and environment. Such systems, even when relatively complicated and expensive, only obtain optimum performance in terms of fuel economy under a limited set of operating conditions.
It is therefore a general object of the present invention to provide a self-adaptive fuel control system that does not depend on prior knowledge of engine performance.
Self-adaptive fuel control systems per se are known and have been discussed by Draper and Li in a publication.* However, the Draper and Li system is designed to provide peak power output (maximum r.p.m.) for any given throttle setting and does not provide maximum fuel economy, as maximum fuel economy occurs near the border-line of lean misfire, not at maximum r.p.m. FNT *C. S. Draper and Y. T. Li, "Principles of Optimalizing Control Systems and the Application to the Internal Combustion Engine", American Society of Mechanical Engineers, 1951.
It is therefore a further object of the present invention to provide maximum fuel economy for any given throttle setting on an internal combustion engine.
A self-adaptive fuel control system that provides maximum fuel economy is described in a U.S. Patent Application entitled "Programmable Fuel Economy Optimizer For An Internal Combustion Engine" by H. E. Riordan, Ser. No. 305,900, filed Sept. 25, 1981 and assigned to the same assignee as is the instant invention. The Riordan fuel economy optimizer provides maximum fuel economy by determining a rate of speed change versus fuel flow rate change and senses the lean limit of the engine on the basis of deceleration rate. This approach, although providing many advantages not possible with prior art fuel control systems, is not compatible with all types of two-cycle engines.
It is therefore a further object of the instant invention to provide a self-adaptive fuel control system that operates with all engine types.
It is another object of the instant invention to provide a self-adaptive fuel control system that provides an exact range of fuel mixture variation.
It is a still further object of the instant invention to provide a self-adaptive fuel control system that has enhanced temperature stability.